This invention relates to the field of transparent coatings for transparent objects such as eyeglass lenses, and refers particularly to a coating compositions having low viscosities and coating compositions producing abrasion-resistant coatings exhibiting high tintability.
Transparent plastic materials such as eyeglass lenses are subject to becoming dull and hazy due to scratching and abrasion during use. Polycarbonate eyeglass lenses, for example, are strong and shatter resistant but also are relatively soft and susceptible to scratching. Television screen face plates similarly are made of flexible, shatter resistant plastic materials such as polycarbonate and poly (methylmethacrylate), and these also can be scratched or abraded.
Various coatings have been proposed for eyeglasses and other transparent plastic materials to reduce their propensity to become scratched and abraded. One such composition is shown in U.S. Pat. No. 4,378,250 (Treadway, et al.) granted Mar. 29, 1983. Other coatings are shown in U.S. Pat. No. 5,367,019 (Sawara), U.S. Pat. No. 4,855,180 (Kawamura), U.S. Pat. No. 4,895,767 (Mori et al.) and U.S. Pat. No. 4,719,146 (Hohage et al.) Besides being abrasion resistant, coatings for eyeglass lenses should also be capable of being tinted by treatment with a dye which becomes incorporated in the coating. As a general observation, the tintability of a coating tends to decrease as its hardness and scratch resistance increases, and vice-versa.
Harasta, et al. U.S. Pat. No. 4,426,431 discusses a coating composition referred to as a xe2x80x9chybridxe2x80x9d system because it employs a solution, in a solvent such as propylene carbonate, of an epoxy compound and a cationic initiator for it, and an acrylic compound and a free radical initiator for it. In general, coating compositions suitable for use in forming protective transparent coatings on eyeglass lenses and the like are provided in solution in a volatile solvent, the solvent serving as a low viscosity vehicle to enable the coating composition to be uniformly spread upon a surface and to accept dye treatments. The solvents that are employed are for the most part organic, and must be used and disposed of carefully.
Perkins et al. U.S. Pat. No. 5,221,560 describes a coating composition containing a polyfunctional, polymerizable non-acrylate functional ether, a radiation-sensitive initiator, and colloidal silica in an amount providing at least 25% by weight of the total solids of the composition, the silica being reacted with a small amount of a hydrolyzed acryloxy-functional or glycidoxy-functional silane.
Treadway, PCT Publication WO 98/39390 describes a coating composition that is substantially free of volatiles and that employs a hydrolysis product of an epoxy-functional silane and also a polymerizable ether. The latter is said to impart tintability to cured coatings of the composition.
U.S. Pat. No. 5,866,262 (Galic et al.) teaches the use of fully hydrolyzed epoxy-functional and imine-functional alkoxysilanes in coating compositions for eyeglass lenses, whereas the previously mentioned U.S. Pat. No. 4,378,250 (Treadway, et al.) teaches that such hydrolysis of epoxy-and imine-functional alkoxysilanes may be less than stoichiometric.
Coating compositions of the type used to provide coatings on such substrates as polycarbonate eye glass lenses desirably are of low viscosity. Moreover, as noted earlier, they desirably are capable, upon curing, of forming surfaces that on the one hand are hard and scratch-resistant and on the other hand are tintable, that is, are capable of readily accepting tinting dyes.
The present invention provides coating compositions yielding cured coatings that exhibit excellent abrasion-resistance and that readily accept tinting dyes. The compositions preferably are of low viscosity and most preferably are substantially free of volatile solvents.
In one embodiment, a composition of the invention comprises the hydrolysis product of an epoxy-functional alkoxy silane, a curing agent therefor, an ethylenically unsaturated monomer and also an unhydrolyzed epoxy-functional alkoxy silane. The ethylenically unsaturated monomer component desirably comprises an acrylic monomer, preferably an acrylic monomer having an acrylic functionality of not more than two.
I have found that inclusion of an unhydrolyzed epoxy-functional alkoxy silane in the coating composition enables a substantial reduction in the viscosity of the composition to be achieved, without loss of abrasion resistance. Amounts of the unhydrolyzed silane sufficient to significantly reduce viscosity of the coating composition up to about 50% by weight, solids basis, are used.
It has also been found that the tintability of coatings derived from a composition comprising the hydrolysis product of an epoxy-functional alkoxy silane, a curing agent therefor and an ethylenically unsaturated monomer, can be substantially improved by incorporating in the composition a non-reactive polyether surfactant.
Hence, the invention in another embodiment relates to a coating composition comprising the hydrolysis product of an epoxy-functional alkoxy silane, a curing agent therefor, an ethylenically unsaturated monomer, and a non-reactive polyether surfactant in sufficient quantity to improve tintability of a cured coating made from the composition. Tintability is so improved by the addition of the polyether surfactant that the coating composition preferably is free of vinyl ethers and reactive non-silane epoxy ingredients. However, as required, the incorporation in the coating composition of non-silane glycidyl ethers may further improve tintability.
The coating compositions of the invention preferably include a cationic initiator such as a diaryl iodonium hexafluoroantimonate and a free radical initiator to initiate polymerization of the ethylenically unsaturated coating components. The composition may include one or more additional epoxy-functional compounds, acrylic monomers, and other ingredients, including colloids, although preferably the composition is free of silica and most preferably is substantially free of colloids.